Objective This paper aims to elucidate the differences between leaf litter decomposition of tree and shrub species in the broadleaved Korean pine forest in Changbai Mountain of northeastern China, explore the relationship of photosynthetic parameters and the decomposition rate of leaf litter, and provide a basis for revealing the universality of leaf economic spectrum.

Method Taking 19 tree and 11 shrub species as research objects, the litter bag method was used for the decomposition experiment. On April 26, June 26, August 26, and October 26, 2020, litter bags were carried out four times in turn. After recovery, the decomposition coefficient was calculated by fitting the Olson negative exponential decay model. At the same time, the light response curve of the in-situ living leaves was measured using the Li-6400 portable photosynthesis instrument, the photosynthetic parameters were fitted, the correlation was analyzed, and regression analysis was performed.

Result (1) Among the arbor species, the decomposition coefficient of Pinus koraiensis was the smallest (0.24), versus the largest for Phellodendron amurense (1.05). The decomposition coefficients of shrub species were larger (or faster) than that of tree species (P = 0.003). Corylus mandshurica had the smallest decomposition coefficient (0.52), and Euonymus verrucosus had the largest (1.63); (2) The photosynthetic parameters were expressed as the net photosynthetic rate at the light saturation point (P_n), stomatal conductance (G_s), leaf carboxylation rate (CE), light saturation point (LSP), and the maximum net photosynthetic rate (P_max), light compensation point (LCP), transpiration rate (T_r), stomatal limit value (L_s), dark respiration rate (R_d), the mean values of the 9 photosynthetic parameters of tree species were higher than those of shrub species (P < 0.05). There was no significant difference in CO₂ concentration (C_i) and water use efficiency (WUE) between tree and shrub species (P > 0.05). (3) Decomposition coefficient (k) showed a significant negative correlation with all physiological properties of leaves, including P_n, LSP, P_max, G_s, CE, LCP, but R_d had no significant correlation. There was multicollinearity between P_n and P_max, and the stepwise regression showed that P_n had the strongest explanatory and indicative effect on k.

Conclusion Light intensity affects the decomposition rate of leaf litter by affecting leaf morphology and nutrient content, resulting in tree species having higher photosynthetic parameters but lower decomposition coefficients than shrub species, i.e. slower decomposition rate. There is a connectivity relationship between light intensity, leaf morphology, nutrient content, and decomposition rate of leaf litter. P_n, G_s, CE, LSP, P_max, LCP basically in line with pectral theory of leaf economics, P_n can explain and predict the decomposition rate of leaf litter.